While our concept of bones as load bearing structural elements stems from well-understood engineering concepts, it is important to realize that most of our engineering knowledge is geared towards solving a different set of problems than those faced by our bodies. The vast majority of structural engineering tasks are focused on constructing stationary structures that maintain a reasonably constant relationship with gravity. In other words, when we build houses (or even moving things like cars and most robots), we generally assume that the structure will stay still and will not perform handstands. Animals, on the other hand, must be robust to any orientation with respect towards gravity. Beyond that, we animals must be able to resist and generate forces into the world from any unexpected direction as we scramble, hunt, run, climb, dance, and play through life.

In general, continuous compression structures are optimized for a single path of forces to flow through them to the ground. As long as the forces the structure will experience over its lifetime are understood, one can build support exactly where it is needed. I’ve always loved the medieval cathedral’s flying buttresses as a good visual image of this.

A Medieval Flying Buttress

The infrastructure that has been built is great for holding the tall walls and roof of the cathedral up. But, if you pushed on the cathedral in an unexpected direction (such as sideways on the middle of the piers as indicated with the arrow below) the structure may fail because it cannot dissipate the applied force.

Due to their integration through the tension network, tensegrity structures are uniquely capable of globally distributing forces and are very robust to forces applied from unexpected directions. In the image below, if one pushes down on the indicated strut, the force is globally distributed through the whole structure. Thus, there is less chance of a single component failing, as all the components share in dissipating the extra force.

This quality makes tensegrity structures tolerant of being reoriented in the field of gravity. While gravity is always applying force in a single direction, how the structure experiences that force is dependant on its orientation relative to the ground. Thus, when we do handstands, the force of gravity is applied to our bodies very differently than when we are standing. Tensegrity structures can deal with this variability in applied forces much better than continuous compression structures.

With Gravity constant, we experience forces from all directions as we move through the world

Many large modern buildings that have large spans or are in earthquake prone regions incorporate concepts from tensegrity structures to take advantage of this robustness to unexpected shaking forces. But beyond that, tensegrity design has not taken over modern construction techniques despite a steady stream of enthusiasm from young architectural and art students. The major problem is that tensegrity structures are not rigid – they oscillate and vibrate as forces integrate through the tension network. Thus, to build static structures such as art sculptures and buildings that will hold still, high levels of tension need to be applied.

But this is exciting! Living animals are never static! We are constantly breathing, moving, vibrating, and oscillating. We are constantly changing our orientation to gravity, and dealing with unexpected forces from every possible direction. These are all properties that tensegrity structures are well suited to deal with. So, my conclusion from all this is that tensegrity structures are an excellent design choice for a something that needs to move, but they are a poor design choice for static rigid structures (other than surprisingly beautiful art). This, of course, all leads back to the Biotensegrity theory that I wrote about last week. (“Introduction to Biotensegrity“)

6 Responses

The example of engineering being mostly concerned with static forces is true, but is this example so because of record available (mainly architecture followed by mechanical examples) or because our technology is so limited yet.

We now have modelling that can handle complex mixing (hydrodynamics) and modeling that can handle complex stresses, but the intellectual framework for tensigrity which would be needed for the computer modelling is not there yet. Or is it? I don’t know.

Yes, there are engineering and modeling techniques to handle complex non-linear systems like tensegrity structures — they are hard, and computationally expensive, but doable. The point is that the “standard” conceptual model of human anatomy is based off of engineering concepts that are really intended for static structures. Thus, it is worth seeing how deeply the conceptual model shifts when thinking about tensegrity structures that are made for motion. The challenge is to figure out how to manage/control tensegrity structures for real-time motion. There has been some research into control of tensegrity based robots already by some pioneering researchers, and I hope to get more in depth on that work soon, along with sharing my vision for how that control should be done.

It would like before everything of congratulating him for the blog, it is excellent.I am physiotherapist and work with Dysfunction of TMJ (Temporomanbular Joint). My patients always present a lot of tension in the musculature chewer and pain. Does the Doctor believe that the use excess (bruxismo) can it also produce an accumulation of collagen in these structures? I have been working my patients always using the acupuncture, mobilization fascial and breathing exercises and he/she would like to understand him/it better because of the results they be so good.

Thanks! Yes — if the patient is holding their jaw clenched (i.e. statically tight) I would expect that muscle to shorten and stiffen, and thus further aggravate the problems. As you mention, fascia mobilization would seem like a good treatment. Of course, while this will help with the pain and the current tightness, the underlying cause as to why the patient is habitually clenching their jaw must still be solved. This will likely have more to do with their psychological response to stress, lifestyle, and general health.

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About BeingHuman

Greetings!
Here you will find my thoughts on being human, based on my ongoing research into robotic and human motion, neuroscience, physiology, and machine learning. You will also find videos of my talks and papers from the Dynamic Tensegrity Robotics Lab which I lead at the NASA Ames Research Center.

Archive of all past posts

Archive of all past posts

My Favorite Ergonomic Equipment

Based on my understanding of human physiology and motion, here are some quick reviews on my favorite ergonomic tools. These are the ones I use at home and at work. I will add more in-depth posts discussing the alignment theory as I get them written.

FitBall Sitting Disc
Sitting Discs are a great way to train for Active Sitting. By destabilizing the surface you are sitting on, they engage your core muscles and keep you in dynamic motion while your body actively balances on the disk. I recommend the larger 15" disc. In Depth Review

Salli Saddle Stool
The Salli saddle stools are one of the best stools for Active Sitting. They hold your pelvis upright, so that your spine can be well aligned with gravity, while also allowing your knees to be lower than your hips to keep your hamstrings and hip-flexors from shortening. Actively sitting takes effort, so increase your time in the saddle slowly.

3M Ergonomic Mouse
The vertical design keeps the arm in a well aligned neutral "handshake" position that prevents the shoulder from rolling forward. By keeping your shoulders back and the scapula flat on your back you avoid many of the common sources of wrist pain. This is the biggest bang for your buck if you are having wrist pain. It comes in small and large sizes (small is linked below). Sadly, I have only seen it for right hands.

ErgoMagic Keyboard
Like the 3M mouse above, this keyboard allows you to have your hands in a more neutral vertical position which reduces many of the problems associated with wrist and shoulder pain. It also allows you to spread the key pads to be at shoulder width so that you don't have to twist your wrist like on a straight keyboard.

Sit-Stand Desk
A sit stand desks allows you to dance while working! It also allows you change between a variety of different sitting options and standing so that you don't get stuck in one position. The best option that I have found is from GeekDesk.com. I have two from them and they are the cheapest and have held up well. You can save even more money by buying just the base frame from GeekDesk and getting the table top from Ikea. You save on price and shipping is significantly less this way.

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Books I Recommend

Sync: How Order Emerges From Chaos In the Universe, Nature, and Daily Life
This book blew my mind.
Really -- this was probably one of the most influential books I've read in a decade. This points straight at the heart of what we intuitively recognize as the difference between living breathing organic aspects of nature and the mechanistic nature of human engineered system. It all boils down to oscillators and their ability to synchronize. This basic mathematical property is the basis for all the order that we see in the world -- and our ability to move -- and our ability to relate to each other -- and really everything. This is an easy and engaging read, and you will come away with new eyes for the world.

Anatomy of Movement
This was the best book I have read for learning about the function of my own body and is endlessly useful for anyone who is alive and moving in the world. Ever have pain when you make a specific motion and wonder what is going on? This book will help you isolate the muscles responsible for that motion. By showing how each muscle moves your body under different conditions, you will learn their *use* rather than just memorizing a bunch of names.

Anatomy Trains: Myofascial Meridians for Manual and Movement Therapists
This book is great to see and understand the complex network of tension in the living body, and to learn about fascia and how it works.

Rhythms of the Brain
This recently published book covers cutting edge theories of how the brain works. The key focus is on how the brain relies heavily on coupled oscillatory networks, timing loops, and synchronization. It also discusses how the activity in the brain can be viewed as a dynamic tensegrity structure. A more technical book, but well worth the effort!